Effect of modified investment and casting system on the recasting properties of high-gold alloy

High gold (Au) alloys have many advantages, such as good mechanical properties and stable chemical properties for dental restoration. The purpose of this investigation was to investigate the effect of zirconia (ZrO₂)-magnesia (MgO)-based investment combined with an argon arc vacuum pressure (Ar-arc VP) casting process on the recasting of high Au alloys.

The recasting Au alloys were compared between the control group of conventional SiO₂-based investment/horizontal centrifugal (HC) casting and the experimental group of ZrO₂-MgO-based investment/Ar-arc VP die casting. The first-generation castings were defined as being made from purchased Au alloys and the second-generation castings were made from 50 wt% of the original Au alloys before casting, plus the balance of the remaining 50 wt% from the previous castings. The third-generation was made from all old surplus from the previous castings. The ingots were measured for the marginal gap, surface roughness, interface oxidation, hardness, and phase identification.

The results showed that the recasting success rate reached 100%. The ZrO₂-MgO-based investment/Ar-arc VP group had better edge precision, smaller oxide layer thickness, and lower hardness than the SiO₂-based investment/HC group. However, surface roughness analysis indicated little difference between the two groups. Phase analysis showed that the recasting alloys of the second and third-generation groups contained higher Au contents than those of the first-generation.

Overall, the Au alloy can be better recasted and retain good mechanical properties under the clinically used 5 wt% ZrO2-MgO-based investment/Ar-arc VP casting method.